This is no bug.
At the moment, only the treeview emits that Event.
Skid mentioned, that he plans to add _GadgetMenu and _GadgetSelect as well to the listbox, but others will never react to it.
You would need to manually do something about it.
I agree that ALL gadgets should react to all 3 events (as gadgetaction on most means doubleclick after the initial activation click)
At the moment, only the treeview emits that Event.
Skid mentioned, that he plans to add _GadgetMenu and _GadgetSelect as well to the listbox, but others will never react to it.
You would need to manually do something about it.
I agree that ALL gadgets should react to all 3 events (as gadgetaction on most means doubleclick after the initial activation click)